VECTOR CODING FOR PARTIAL RESPONSE CHANNELS

The combination of equalization and coding for the additive Gaussian noise channel with linear intersymbol interference (ISI) has received attention recently. A linear technique for combining equalization and coset codes on partial response channels with additive white Gaussian noise is developed. The technique, entitled “vector coding”, uses a set of transmit Filters or “vectors” to partition the channel into an independent set of parallel ISI-free channels for any given finite (or infinite) block length. The optimal transmit vectors for such channel partitioning are shown to be the eigenvectors of the channel covariance matrix for the specified block length, and the gains of the individual channels are the eigenvalues. An optimal bit allocation and energy distribution are derived for the set of parallel channels, under an accurate extension of the “continuous approximation” for power in optimal multidimensional signal sets for constellations with unequal signal spacing in different dimensions. Examples are presented that demonstrate performance advantages with respect to zero-forcing decision feedback methods that use the same coset code on the same partial response channel. Only resampling the channel at an optimal rate, and assuming no errors in the feedback path, will bring the performance of the decision feedback methods up to the level of the vector coded system. © 1990 IEEE